Multifocal lens having an optical add power progression, and a system and method of providing same

ABSTRACT

An apparatus, system and method including an ophthalmic lens having an optic with an anterior surface, a posterior surface, and an optical axis. The ophthalmic lens further includes a first region having a first optical power and a second region having a second optical power. The ophthalmic lens further includes a third region having an optical power that progresses from the first optical power to the second optical power. The progression may be uniform or non-uniform. Each of the first, second and progression optical power may include a base power and an optical add power. Each of the first, second and progression regions may provide a first focus, a second focus and a plurality of third foci, respectively.

CROSS-REFERENCE TO RELATED PATENTS AND APPLICATIONS

The present application claims priority under 35 U.S.C §119(e) toprovisional application No. 61/418,759, filed on Dec. 1, 2010, which isincorporated herein by reference in its entirety. Full Paris Conventionpriority is hereby expressly reserved.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates generally to ophthalmic lenses, and morespecifically to a multifocal ophthalmic lens having an optical add powerprogression, as well as a system and method for providing such amultifocal ophthalmic lens.

Description of the Background

An ophthalmic lens, such as an intraocular lens (IOL), a phakic IOL, ora corneal implant, by way of non-limiting example, may be used toenhance patient vision. For example, an IOL may be used to replace thenatural lens of an eye that is removed during cataract surgery.

Multifocal lenses, including multifocal IOLs, may replace the functionof the eye's natural lens in providing multifocal vision, such as bydividing incident light to two different focal points to provide bothnear and distance vision. The use of diffractive or refractive optics inophthalmic lenses, in order to provide multifocal/bifocal division ofincident light, is well understood to those skilled in the pertinentarts.

In a bifocal IOL, the optic area may be divided into a plurality ofannular zones that are offset parallel to the optical axis to provide aspecific diffractive or refractive relationship between the zones. Asused herein, “annular” is defined to be ring-shaped, substantiallyring-shaped, or at least partially ring-shaped. The annular zones mayform a concentrically arranged pattern characterized by the opticalpower step between zones, the circumferential spacing between zones, andthe surface profile of each zone. These concentric annular zones aretypically configured to maintain a predefined relationship of lightpassing through the zones to effect bifocal vision. Unfortunately, theabrupt optical power step between zones makes it difficult for such asolution to provide improved far and near vision simultaneously, whileavoiding glare, halos, decreased contrast sensitivity, and increasedpupil dependence. Further, such solutions are not designed to achieveintermediate vision, which would optimally correct presbyopia.

In known alternative embodiments of a multifocal lens, the zones may benon-radially symmetric (see the Lentis MPlus® lens by OcuLentis), suchas in the embodiment illustrated in FIG. 1 as 23 b. More particularly,center and upper zones may be at least substantially circular andsemi-circular respectively, and may have thereabout below a portionhaving a different optical power than the center and upper zone. In sucha lens, the upper and central portion of the optic may be used fordistance vision, and the optical add power may be constrained to thelower portion of the lens, in the non-radially symmetric distribution,as would be the case for a bifocal spectacle lens. As used herein, theterm “non-radially symmetric” is used to indicate that the distributionis not the same for all the points at the same distance from the centerof the optic in the lens plane.

As such, the zones of these exemplary bifocal IOLs may form a bifocallens that may, for example, produce a first focal point for distantvision, and a second focal point corresponding to near distances. Apreferred characteristic of lenses that incorporatediffractive/refractive zones in this manner is that the amount of lightin the near and distant foci be substantially constant for all pupilsizes. However, it might be desired in certain instances to increase theamount of light in the distant focus as the pupil size increases, forinstance under intermediate or low light conditions. One way to increasethe amount of light dedicated to distance vision is to restrict the zoneproducing the second focal point to the central portion of the lens, andto make the outer region of the lens refractive only.

A particular disadvantage associated with the radially symmetric-type ofbifocal IOL is the aforementioned problem of halos. In the case ofhalos, light from the unused foci creates an out-of-focus image that issuperimposed on the used foci, in part due to the abrupt change inoptical power between adjacent ones of the annular zones. For example,if light from a distant point source is imaged onto the retina of theeye by the distant focus produced by a concentric bifocal IOL, the nearfocus produced by that IOL may simultaneously superimpose a defocusedimage on top of the image formed by the distant focus, thus creating ahalo effect. Thus, it is not possible to have high contrast imageseither at the far focus or near focus. Although non-radially symmetricIOLs may partially address halos, such halos are constrained to the partof the field of view where the added power is addressed. In addition,the abrupt optical power changes between zones preclude completeelimination of halos and glare.

Therefore, the need exists for a lens, and a system and method ofproviding a lens having an optical add power progression that allows forthe following: far, near and intermediate vision with good visualperformance at all distances; significantly reduced halos and glare;improved contrast sensitivity; and minimized pupil dependence.

SUMMARY OF THE INVENTION

The aspects of the apparatus, system and method of the present inventioninclude an ophthalmic lens having an optic with an anterior surface, aposterior surface, and an optical axis. The ophthalmic lens furtherincludes a first region having a first optical power and a second regionhaving a second optical power. The ophthalmic lens further includes athird region having optical powers that progress from the first opticalpower to the second optical power. The progression may be uniform ornon-uniform. Each of the first and second zones may include a base powerand an optical add power. Each of the first, second and progressionregions may provide a first focus, a second focus and a plurality ofthird foci, covering far, near and intermediate distances, respectively.

More particularly, an ophthalmic lens in accordance with the presentinvention may include an optic comprising a first region having a baseoptical power and a first optical add power for providing a first focus,a second region having the base optical power and a second optical addpower different from the first optical add power for providing a secondfocus and a third region having the base optical power and a thirdoptical add power comprising a progression of optical add power from thefirst optical add power to the second optical add power.

In an exemplary embodiment where the power progression is appliedvertically, the first region may comprise an uppermost portion of theoptic, and may provide a distance vision focus. The uppermost portionmay comprise at least the uppermost about 37.5% to 50% of the opticalong a vertical diameter of the optic. The second region may comprise alowermost portion of the optic, and may provide a near vision focus. Thelowermost portion may comprise at least the lowermost about 25% of theoptic along the vertical diameter of the optic. The third region maycomprise a central portion of the optic occupying at least thecentralmost about 25% of the optic along a vertical diameter of saidoptic.

The regional divisions of the lens may be chosen to either decreasepupil dependence or enhance determined viewing distances and allow for aproper far focus determination in the refraction procedure, usuallyperformed at photopic light level conditions. More particularly and byway of non-limiting example, in a central 3 mm diameter area, theuppermost approximately about 25%-50% of the optic along a verticaldiameter may be defined to achieve far vision, and the completeprogression between the far and near addition may occur in the remainingpart of the lens between the near and far vision. Other alternativeembodiments are envisioned herein, including variations in regionalpower distributions and added powers. The regional power distributionsmay also be considered in the vertical or horizontal direction, or incombinations thereof.

A method of providing a progressive intraocular lens according to thepresent invention may include assessing at least one biometric of asubject eye, assessing a vision correction and at least a multifocalcorrection required for the subject eye, and indicating a set ofintraocular lenses with each lens in the set having at least one opticaladd power region with the same base power for remedying the visioncorrection, and different optical add power progressions therebetweenfor providing the multifocal correction, wherein the at least onebiometric indicates at least one in situ aspect of the intraocular lens.The method may further include simulating the optical quality of thepatient's eye once implanted with each intraocular lens from that setand selecting the intraocular lens with the corresponding powerprogression that maximizes patient eye's optical quality.

The method of providing a progressive intraocular lens according to thepresent invention may be customized. For example, far vision may beachieved by a base power calculated considering the biometric eye data,the near addition may be customized considering typical visual taskscarried out by the patient, and the intermediate addition may be apersonalized progression.

A lens system for providing multifocal vision correction, according tothe present invention, may include a first focal region, a second focalregion and a third region, physically distinct from at least the firstfocal region and the second focal region. The third region may provide aplurality of third foci representing a progression of optical add powerbetween a first optical add power of the first focal region and a secondoptical add power of the second focal region. All regions may be joinedin a continuous through focus curve that allows for simultaneous far,near and intermediate vision, with a similar optical quality.

Thus, the present invention provides a lens, and a system and method ofproviding a lens, having an optical add power progression that allowsfor vision across a range of distances with improved contrastsensitivity, while minimizing halos and glare and pupil dependence.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention will be understood with referenceto the detailed description in conjunction with the accompanyingfigures, in which like numerals indicate like aspects, and wherein:

FIG. 1 is a schematic illustration of combinations of prior art bifocallenses;

FIG. 2 is a schematic illustration of an eye having implanted therein anintraocular lens viewing an object at infinity;

FIG. 3 is a schematic illustration of an eye having implanted therein anintraocular lens viewing an object at a near distance;

FIG. 4 is a schematic illustration of an intraocular lens havingmultiple annular zones;

FIG. 5 is a schematic illustration of a multifocal intraocular lenshaving a vertical optical power progression;

FIG. 6 is the sag representation of an embodiment in comparison with twolenses with a fixed power;

FIG. 7 is the difference between the lens surface result of a preferredembodiment and the surface of a 20D lens;

FIGS. 8a and 8b are the simulated through focus MTF in the tangentialand sagital direction for the design corresponding to FIG. 7 fordifferent entrance pupils once implanted in an average eye model incomparison to that provided by a marketed lens;

FIG. 9 is a list of Zernike coefficients corresponding to the same eyemodel as in FIG. 8a for 6 mm entrance pupil at 540 nm;

FIGS. 10a and 10b is the difference between the lens surface result ofan alternative embodiment and the surface of a 21D lens and 20Drespectively;

FIGS. 11a and 11b are the simulated through focus MTF in the tangentialand sagital direction for the design corresponding to FIG. 10 fordifferent entrance pupils once implanted in an average eye model incomparison to that provided by a marketed lens;

FIG. 12 is a list of Zernike coefficients corresponding to the same eyemodel as in FIG. 11a for 6 mm entrance pupil at 540 nm;

FIG. 13 is the difference between the lens surface result of anotheralternative embodiment and the surface of a 21D lens and 20Drespectively;

FIGS. 14a and 14b are the simulated through focus MTF in the tangentialand sagital direction for the design corresponding to FIG. 13 fordifferent entrance pupils once implanted in an average eye model incomparison to that provided by a marketed lens;

FIG. 15 is a list of Zernike coefficients corresponding to the same eyemodel as in FIG. 14a for 6 mm entrance pupil at 540 nm;

FIG. 16 is a schematic illustration of a multifocal intraocular lenshaving a curved optical power progression;

FIG. 17 is a table showing the pupil dynamic of the design presented atFIG. 5;

FIG. 18 is a flow diagram illustrating a method of providing anintraocular lens; and

FIG. 19 is a graphical representation of the elements of computingsystem for selecting an intraocular lens.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for the purpose of clarity, many other elements found in typicalimplantable optic apparatuses, systems and methods. Those of ordinaryskill in the art may thus recognize that other elements and/or steps aredesirable and/or required in implementing the present invention.However, because such elements and steps are well known in the art, andbecause they do not facilitate a better understanding of the presentinvention, a discussion of such elements and steps is not providedherein. The disclosure herein is directed to all such variations andmodifications to the disclosed elements and methods known to thoseskilled in the art.

The present invention is directed to apparatuses, systems and methodsfor providing and/or designing a multifocal ophthalmic lens, such as amultifocal intraocular lens (IOL), that provides varied optical power toenhance vision for different focal distances. The terms “power” and“optical power”, as used herein, are defined to include the capabilityof an optical surface to redirect incident light to a focal point. Theoptical power may result from reflection, refraction, diffraction, orsome combination thereof, and is generally expressed in units ofDiopters.

FIG. 2 illustrates a bifocal IOL 20 with an optical axis 21 disposed inan eye 22. Annular zones 23 for varying optical power are concentricallydisposed on an anterior surface 24 having a base curvature, C, and areilluminated by incident light 26 from a distant object that enters theeye 22 in the form of collimated light. Annular zones may be similarlydisposed on a posterior surface 28 of lens 20, or on a combination ofthe anterior and posterior surfaces of lens 20.

A first portion 27 of the incident light 26 may be substantiallyunaffected by zones 23, or may be affected by some of zones 23, and maybe focused to produce a first focus 29 approximately located on a retina30 of the eye 22. This first focus 29 provides distant vision. A secondportion 32 of the incident light 26 may form a second focus 34, locatedin front of the retina. IOL 20 thus effectively has at least two opticalpowers due to the combination of the anterior surface 24, the posteriorsurface 28, and zones 23.

As used herein, the term “near vision' generally corresponds to visionprovided when objects are at a distance between about 25 cm to about 50cm. Conversely, the terms “distance vision” and “distant vision,” asused herein, refer to vision wherein objects viewed are relatively farfrom the subject. The terms “distance vision” and “distant vision” maythus generally correspond to vision provided when objects are at adistance of at least about 2 meters or more away from the subject. Theterm “intermediate vision” refers herein to the viewing of objects at adistance between near vision and distant vision.

FIG. 3 illustrates the performance of IOL 20 for a near object 40located relatively close to the eye 22. Under these conditions, thedistant and near foci 29 and 34, respectively, provided by optic 45 aredisposed such that the near focus 34 is approximately located on theretina 30 and the distant focus 29 is approximately located behind theretina 30. Thereby, IOL 20 may function as a bifocal lens that providesa patient with both near and distant vision.

FIG. 4 shows a multifocal lens that provides the optical behaviorpreviously discussed. The plurality of annular zones 23 a that providethe bifocal lens functionality may have a particular offset betweenadjacent zones along the center of the lens. The bifocal characteristicsof IOL 20 may be realized, for example, by selecting the offset betweenadjacent zones to be such that rays to either side of the offsetexperience a difference in optical path length.

Lens 20 may be an intraocular lens for placement in either the posterioror anterior chamber of a subject eye. As such, lens 20 may be used toreplace the natural lens of the eye, such as after removal of thenatural lens during cataract surgery. Alternatively, the lens 20 may bea phakic lens disposed in front of the iris, behind the iris, or in theplane defined by the iris. Alternatively, lens 20 may be a cornealimplant. Alternatively, lens 20 may be a contact lens or the like usedto provide or improve vision.

Lens 20 may be constructed of any commonly employed material ormaterials used for optics, such as polymethylmethacrylate (PMMA),silicone polymeric materials, acrylic polymeric materials,hydrogel-forming polymeric materials, such aspolyhydroxyethylmethacrylate, polyphosphazenes, polyurethanes, mixturesthereof, and the like. The construction material preferably is capableof providing the requisite vision or vision correction, and exhibitsbiocompatibility with the eye. Lens 20 may be made of or containphotosensitive materials (e.g., photopolymer or silver halide) or avariable refractive index material.

Foldable/deformable materials are particularly advantageous for use inor as lens 20 and/or optic 45, since such deformable materials may berolled, folded or otherwise deformed and inserted into the eye through asmall incision. The lens material preferably has a refractive indexallowing a relatively thin, and preferably flexible, optic 45, forexample, having a thickness in the range of about 100 microns to about1000 microns, and preferably about 150 microns to about 500 microns. Inembodiments wherein lens 20 is an intraocular lens, optic 45 may have adiameter of about 2 mm or less to about 7 mm or more, and preferably ofabout 4.0 mm to about 6.0 mm or about 6.5 mm.

In an exemplary embodiment, lens 20 may comprise one or more fixationand/or support members, or “haptics.” Haptics 47 may be made of the samematerial as optic 45 and/or may be integrally formed with optic 45.Alternatively, one or more haptics 47 may be formed separately andattached to optic 45. Haptics 47 may comprise any of a variety ofmaterials that exhibit sufficient supporting strength and resilience,and/or that are substantially biologically inert in the intended in vivoor in-eye environment. Suitable materials for this purpose include, forexample, polymeric materials such as silicone polymeric materials,acrylic polymeric materials, hydrogel-forming polymeric materials, suchas polyhydroxyethylmethacrylate, polyphosphazenes, polyurethanes,mixtures thereof, and the like.

As illustrated in FIG. 4, annular zones 23 a typically include a centralzone 134 that is at least partially annular and that is surrounded byanother zone or zones 130 that typically have an at least partiallyannular shape. Whether the add power is achieved via refraction ordiffraction, determination of the diameter and height of each of theannular zones 130, 134 is well known in the art and is generally afunction of a design wavelength and the desired focal lengths of lens20. In prior art embodiments of FIG. 4 which reflects refractivetechnology, each annular zone is provided with a particular opticalpower, and, to the extent a different focal length is to be provided byothers of the annular zone(s) from the first annular zone, those othersof the annular zone(s) may be suitably provided with a different opticalpower than the optical power of the first annular zone.

The annular zones 130, 134 are preferably concentrically offset in theIOL plane so as to form optical add power steps between adjacent zones130, 134, the steps being selected to produce a predefined relationshipbetween each of the annular zones 130, 134. In certain embodiments, thezones 130 are formed by refractive index variations between the centralzone 134 and the other zones 134. Preferably in the embodiment of FIG.4, the variation in refractive index across the surfaces is in a radialdirection from the center of the optic.

However, the abrupt changes in the optical add power steps betweendifferent zones 130, 134 of the lens 20 typically generate glare and/orhalos, with loss in contrast sensitivity. This is amplified whendiffraction is used to generate an extra foci due to the amount of lightthat is lost in diffraction orders other than those used to achievemultifocality. In addition, intermediate vision is not adequatelyprovided by these types of designs, in part because the design is forenhancing only near and far vision.

To remedy these disadvantages of the prior art, the present inventionprovides a design with at least three different zones that providemultifocal vision. An exemplary embodiment is presented in FIG. 5, whichshows a lens 20 having three distinct zones 210, 220, 230 that providemultifocal vision. Of note, the dotted line on the lens of FIG. 5illustrates a central zone (which is 3 mm in diameter in the illustratedexemplary embodiment), rather than illustrating a physical geometricsurface feature of lens 20 or a uniform region for optical power. Offurther note, zones 210, 220 and 230 may be concentrically ornon-concentrically annular, or, as discussed further hereinbelow,horizontal, vertical, oblique or curved. The extension of the differentzones can be modified such that any zone may be eliminated or providedwith a zero add power in order to enhance the visual acuity at varyingdistances as required for the patient.

Zones 220, 210, 230 are distinct from zones 130, 134, at least in thatthere is no abrupt change in optical power as between illustratedcentral zone 210 and zones 220, 230. More particularly, the optical addpower progressively varies across at least a portion of lens 20, andsuch progression may occur concentrically outward from the center pointof central zone 210, vertically from a top portion to a bottom portionof the optic of lens 20 as that lens resides in situ, horizontally froma right to left portion of the optic of lens 20 as that lens resides insitu, and/or in any combinations thereof.

By way of example, when the design is applied vertically, lens 20 mayhave an optic with a particular diameter, such as 6 mm. From the top ofthe optic as the optic is positioned in situ, at 37.5% from the topmostpoint along the vertical diameter, or 2.25 mm along the verticaldiameter from the top of a 6 mm diameter exemplary optic, 0 Diopters ofoptical add power may be provided for all horizontal cross sectionsacross optic 45. For the next 2.25 mm along the vertical diameter of anexemplary 6 mm diameter optic, the optical add power may verticallyprogress from 0 Diopters to, for example, about +3 Diopters. Along thelowermost portion of optic, such as the lowermost 25% along the verticaldiameter (i.e., the lowermost 1.5 mm of the vertical diameter of anexemplary 6 mm diameter optic 45), the optical add power may remainconstant, such as at +3 Diopters, for example, or alternatively mayfollow a secondary progression. The vertical progression(s) may progressat a substantially uniform, constant rate, or may progress at varyingrates.

The zone 210 is designed to be non concentric with respect the optic.Considering the 3 mm inner part of the optic, the 25% is included in thezone 220 while the remaining 75% is inside of the zone 210.

For the sake of clarity, as used herein the optical add power is theadditional optical power provided in conjunction with a base power forthe optic. Of course, those skilled in the art will appreciate, in lightof the discussion herein, that the base power of the optic may becalculated in order to achieve emmetropia for far distances.

For a determined regional power distribution, the method by which thepower progresses can be defined as follows. In an embodiment, assuming aconstant progression of power between the designed for boundaries ofoptical add power, the horizontal cross-sectional add power in thisillustrative 6 mm diameter optic embodiment may follow the equation:

0 D 0 < y′ < 2.25 mm 1.33*(y′ − 2.25) D 2.25 < y′ < 4.5 mm 3 D y′ > 4.5mm

where y′ is the distance from reference 0 mm at the top of the verticaldiameter of the optic. Thus, the add power along a horizontal crosssection through the center point of optic (i.e., where y′=3) is, in thisexemplary embodiment:

1.33*(3−2.25)=1.00 D. In alternative embodiments, y′ may be measuredfrom other points at the edge of the optic, e.g. at the far right pointof the horizontal diameter of the optic.

The same horizontal cross sectional add power may be expressed bymeasuring the vertical distance from the center of the lens:

0 D −3 < y < −0.75 mm 1.33*(y + 0.75) D −0.75 < y < 1.5 mm 3 D y > 1.5mmwhere y represents the vertical distance with respect to the center ofthe lens. Such a power distribution is identical to that previouslypresented.

In another embodiment with the same regional power distribution, themethod of designing the progression might be imposed by a step function.In that case, the power may be as follows:

+0D 0 < y′ < 2.25 mm +1D 2.25 < y′ < 3.375 mm +2 D 3.375 < y′ < 4.5 mm+3 D 4.5 < y′ < 6 mmwhen the vertical distance (y′) is measured from the uppermost part ofthe lens or:

+0 D −3 < y < −0.75 mm +1D −0.75 < y < 0.375 mm +2 D 0.375 < y < 1.5 mm+3 D 1.5 < y < 3 mmwhen y represents the vertical distance to the center of the lens.

FIG. 6 shows the sag corresponding to two aspheric lenses with differentpower (ie. 20D and 23D). The sag of the progressive design correspondingto the previous embodiment when the base power is 20D is alsorepresented in that plot. In this context, base power is the powerproviding far vision. Thus, in this particular example, the progressivelens is composed by the curvatures of 20D, 21D, 22D and 23D, accordingthe previous power profile. FIG. 6 shows how the sag progressivelychanges from that corresponding to a 20D, in the uppermost part of thelens, to that related to a 23D, in the lowermost part of the lens.Therefore, the addition of +3D is achieved, by following the progressiondescribed in the previous embodiment.

The tangential sag defined in such a way may be then fitted according to(eq 1):

${z(y)} = {\frac{{cy}^{2}}{1 + {\sqrt{1 - {\left( {k + 1} \right)y^{2}}}c^{2}}} + {k\; 1y} + {k\; 3y^{3}} + {k\; 4y^{4}} + {k\; 5{y^{5}++}k\; 6y^{6}} + {k\; 7\; y^{7}} + {k\; 8y^{8}}}$Therefore, the vertical meridian of the lens is defined according to anextended aspheric shape, with a curvature c and a conic constant k,although other symmetrical or non symmetrical terms (k1 until k8) areconsidered in order to achieve the fitting of the corresponding surface.The exemplary embodiment showed in FIG. 6, may be fitted according theprevious formula selecting the curvature and conic constantcorresponding to the base power (20D in the exemplary embodiment). Theresults of that fitting define the tangential sag of the lens. Tofurther define the complete design, an extended biconic surface is used(eq. 2):

${z\left( {x,y} \right)} = {\frac{{cy}^{2} + {cx}^{2}}{\left. {1 + {\sqrt{\left( {1 - {\left( {k + 1} \right)y^{2}}} \right.}c^{2}} - {\left( {k + 1} \right)x^{2}c^{2}}} \right)} + {k\; 1y} + {k\; 3y^{3}} + {k\; 4y^{4}} + {k\; 5{y^{5}++}k\; 6y^{6}} + {k\; 7y^{7}} + {k\; 8y^{8}}}$Thus, the curvature and conic constant used for fitting the tangentialsag are also considered in generating the corresponding meridional sag,which is defined as a standard aspheric surface, defining thecombination of the complete surface of the lens. FIG. 7 presents thedifference in shape between the exemplary design and the base power lens(ie. 20D). This difference is zero in the uppermost part of the lens,while the difference increase with the vertical distance. Therefore, themethod herein described provides a lens design that corresponds to FIG.5, when a step power progression is imposed.

The optical behavior of such a design can be computationally tested.Those skilled in the art will appreciate that, for example, an opticaldesign software simulation may be employed in order to provide suchmodeling, for example, using Zemax® software by Zemax DevelopmentCorporation of Bellevue, Wash. A computational model of an average eyemay be used in order to evaluate the performance of the design. Thiscomputational model may comprise the most representative opticalstructures of the eye, such as the cornea, the pupil and the retina.Average corneal aberrations may also be considered in order to furthermimic the average eye. An IOL with a determined design may be insertedin such a model and different optical quality parameters may becalculated. Those calculations may be performed in white lightconditions to closely represent the real behavior of the design, onceimplanted into the eye.

FIGS. 8a and 8b illustrate the tangential and sagittal modulationtransfer function (MTF) at 30 cycles per millimeter calculated fordifferent vergences in such a model eye with the exemplary designdescribed above for two different entrance pupils. For comparisonpurposes, the through focus MTF of a monofocal lens is also shown.

The optical quality of the eye containing the progressive design mayalso be assessed by the eye's model wavefront aberrations. FIG. 9 liststhe Zernike terms until 6^(th) order calculated at 6mm entrance pupilfor 540 nm. It is understood that the design generates some amount ofnon symmetrical aberrations, such as astigmatism, coma and trefoil.

The design represented at FIG. 5, with the vertical regional powerdistribution described before and comprising a step power progressionmay have variants. In another embodiment, the same sag (i.e. the sameoptical power progression) as presented in FIG. 6 may also be fitted toeq 1 according to a different power. Thus, the curvature and conicconstant may be different to that defining the lens' base power. In thatcase, the curvature and conic constant considered to fit the verticalpower progression may also be used in the x direction in order togenerate the extended biconic surface which defines the design,according eq 2.

Thus, in an alternative exemplary embodiment, the sag at FIG. 6, thathas 20D as base power, may be fitted using the curvature and conicconstant for a 21D lens, according to eq. 1. The corresponding lenssurface is generated therefore using an extended biconic surface that inthe x direction is defined by the radius and conic constantscorresponding to 21D and according to the achieved fitting in the ydirection, as stated in eq. 2.

FIG. 10a shows the difference between such a design and the surfacedefining the curvature and conic constant, which is that correspondingto a 21D lens. FIG. 10b shows the difference between that exemplarydesign and the surface of a 20D lens, that is the base power lens. FIGS.11a and 11b show the tangential and sagittal through focus MTFcalculated in the same eye model as previously described when thisexemplary design is inserted. FIG. 12 presents the wavefront aberrationsof the eye at 6 mm entrance pupil for 540 nm. Those skilled in the artmay appreciate that this alternative embodiment introduces some amountof non symmetrical aberrations, although the amount of inducedastigmatism is lower than in the previous exemplary embodiment,presented at FIG. 9. Therefore, the present embodiment of the inventionis a power progression lens with reduced astigmatism induction.

In another alternative embodiment, the curvature and conic constantcorresponding to the x direction may be different to that defining thetangential progression. Thus, the surface is represented by eq. 3:

${z\left( {x,y} \right)} = {\frac{{c_{y}y^{2}} + {c_{x}x^{2}}}{\left. {1 + {\sqrt{\left( {1 - {\left( {k_{y} + 1} \right)y^{2}}} \right.}c_{y}^{2}} - {\left( {k_{x} + 1} \right)x^{2}c_{x}^{2}}} \right)} + {k\; 1y} + {k\; 3y^{3}} + {k\; 4y^{4}} + {k\; 5{y^{5}++}k\; 6y^{6}} + {k\; 7y^{7}} + {k\; 8y^{8}}}$where the cx and kx and cy and ky are the curvature and conic constantrespectively in the x and y direction.

The power progression concept herein described may be applied inorientations other than vertically. In an alternative embodiment, theresults from the fitting corresponding to the sag of the powerprogression may also be used to generate an additional progression inthe x direction, according to eq 4:

${z\left( {x,y} \right)} = {\frac{{c_{y}y^{2}} + {c_{x}x^{2}}}{\left. {1 + {\sqrt{\left( {1 - {\left( {k_{y} + 1} \right)y^{2}}} \right.}c_{y}^{2}} - {\left( {k_{x} + 1} \right)x^{2}c_{x}^{2}}} \right)} + {k\; 1_{y}y} + {k\; 3_{y}y^{3}} + {k\; 4_{y}y^{4}} + {k\; 5_{y}{y^{5}++}k\; 6_{y}y^{6}} + {k\; 7_{y}y^{7}} + {k\; 8_{y}y^{8}} + {k\; 1_{x}x} + {k\; 3_{x}x^{3}} + {k\; 4_{x}x^{4}} + {k\; 5_{x}{x^{5}++}k\; 6_{x}x^{6}} + {k\; 7_{x}x^{7}} + {k\; 8_{x}x^{8}}}$where the kix and kiy with i=1,8 are the results from the fittingrepresenting the power progression in the x and y direction respectivelywith respect to the curvatures and conic constants cx and kx, and cy andky respectively. Those skilled in the art may understand that the powerprogression applied in the x and y direction may be the same, fitted ornot against the same base power, or may be different.

In an exemplary embodiment, the progressive surface is generated byapplying the power progression corresponding to FIG. 6 fitted againstthe 20D in the x direction. In the y direction the same powerprogression is applied but fitted against 21D. Thus, this is a doubleprogression (ie. in the x and y direction), defined according eq 4, withtwo different curvatures and conic constants respectively in x and y.FIG. 13 shows the difference between this surface and a 20D and 21Drespectively. Such a surface represents a curved power progression.FIGS. 14a and 14b represent the optical quality of the model eyepreviously described once implanted with the lens herein described. FIG.15 lists the Zernike coefficients of the eye model once implanted withthe herein showed design.

The step progression which defines the sag at FIG. 6 may be representedby more steps with, alternatively, different powers. The methoddescribing the tangential fitting and the biconic surface generation mayalso be applied to that alternative power progression.

The minimum or maximum add power of the exemplary embodiment are merelyillustrative. More particularly, the minimum add power may be greaterthan 0 Diopters, and/or the maximum add power may be less than orgreater than +3 Diopters. For example, the minimum or maximum add powermay be modified to provide a customized performance for near,intermediate or distance vision of the subject.

Likewise, the point along the diameter at which the progression beginsor ends may be modified, such as in order to customize performance ofthe optic. Moreover, multiple progressions may occur along the diameter,such as wherein a progression is implemented from 0 mm to 2.25 mm in theexemplary 6 mm diameter optic, the same or a different progression isimplemented from 2.25 mm to 4.5 mm, and the same, or yet a different,progression is implemented from 4.5 mm to 6 mm. Similarly, one or allprogressions may be uniform progressions, or may be non-uniformprogressions, in order to customize the vision outcome by subject. Thepower addition progression may be displaced with respect the center ofthe optic.

With reference to FIG. 5, an exemplary embodiment is discussed in whichadd power is constant along each horizontal cross section. Those skilledin the art will appreciate that the add power may be constant along acurve, rather than along a horizontal cross section, as illustrated inFIG. 16. Similarly, zones 210, 220, 230 may be provided concentricallyand, in such a case, add power may be constant along a curve, and/or maybe non-constant along a horizontal cross section of optic 23 c, asoccurs in the design corresponding to FIG. 13.

In the present example, the power addition progression is displaced withrespect the center of the optic. By this way, pupil independence isaddressed. It is important to note that the far focus should be clearlyappreciable by the patient in order to avoid near dependent designs thatcould lead to confusion for the subject in the far focus finding duringthe refraction process, thus eliminating the multifocal effect of theoptic.

FIG. 17 illustrates the behavior of the optic presented at FIG. 5 withrespect to the physical pupil size. As shown, for a 3 mm pupil, far andintermediate viewing distances may be enhanced. As the pupil sizeincreases to 4 mm, both the near and far viewing distances are enhancedto the same or substantially same ratio, thus indicating that the designof the present invention may be pupil independent. Further, for largerpupils, near focus may be particularly enhanced with respect to farand/or intermediate focus.

It will be appreciated that confining the add power progression to thecentral zone, in accordance with the present invention, may avoidsignificant pupil dependence. Further, the add power progression mayavoid abrupt power changes that can lead to halos, glare and decreasedcontrast sensitivity, while being particularly beneficial forintermediate vision.

Although an optical add power progression in accordance with the presentinvention may cause astigmatism, coma, and/or other aberrations, acustomized simulation executed prior to implantation may allow foranticipation of such aberrations, and may indicate one or more designselections, as discussed herein, in order to maximize the opticalperformance of the coupling between the design and those aberrationsadded by the patient.

FIG. 18 illustrates a method 250 of implementing the invention discussedhereinthroughout. The method 250 may include the steps of assessing thebiometric measurements of the eye at step 252, such as to define a basepower to achieve emmetropia at far distance at step 253. Further, step252 may include questions related to the patient's life style (commonhabits, work, etc.), such as to define an optimal near power addition atstep 254. The output of steps 252, 253 and 254 may, in combination,allow for a determination of the regional power distribution at step255. Step 256 may additionally include further designs, such as forparticular enhancement of far, near and/or intermediate vision, asherein described. At step 257, simulations may be used to indicate anyaberrations resulting from the add power progressions at steps 256 andits impact when introduced into the patient's eye, and at step 257 aselection between all possible designs is made according to priorsimulations, leading to the final customized lens design. Those skilledin the art will appreciate that certain of the steps of method 250 maybe performed using computing and/or simulations.

More particularly, and as illustrated in FIG. 19, the present inventionmay be implemented in a clinical system 300 that is capable of assessingthe eye's biometric measurements and of performing the calculations setforth in method 250. The system 300 may include a biometric reader 301that may take or formulate measurements needed for at least a base powercalculation 301, a processor 302, and a computer readable memory 304coupled to the processor 302. The computer readable memory 304 includestherein an array of ordered values 308 and sequences of instructions 310which, when executed by the processor 302, cause the processor 302 todesign an IOL and power progression of the IOL configured forimplantation into the eye of the subject presenting the biometricreadings to biometric reader 301. The array of ordered values 308 maycomprise data used or obtained from method 250 or other methodsconsistent with embodiments of the invention. The sequence ofinstructions 310 may include one or more steps of method 250 or othermethods consistent with embodiments of the invention.

The processor 302 may be embodied in a general purpose desktop or laptopcomputer, and/or may comprise hardware associated with biometric reader301 specifically for selecting an IOL having an add power progressionfor placement into the eye of the subject. In certain embodiments, thesystem 300 may be configured to be electronically coupled to anotherdevice, such as one or more instruments for obtaining measurements of aneye or a plurality of eyes. Alternatively, the system 300 may beembodied in a handheld device that may be adapted to be electronicallyand/or wirelessly coupled to one or more other devices.

Those of ordinary skill in the art may recognize that many modificationsand variations of the present invention may be implemented withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention covers such modifications andvariations of this invention provided they come within the scope of thediscussion herein and any appended claims, and any equivalents thereto.

The invention claimed is:
 1. An ophthalmic lens, comprising: an optichaving a vertical diameter and a horizontal diameter, comprising: afirst region having a first optical power for providing a first focus,wherein the first region comprises an uppermost portion of said opticand wherein the first optical power is constant along each horizontalcross section in the first region; a second region having a secondoptical add power different from the first optical power for providing asecond focus, wherein the second region comprises a lowermost portion ofsaid optic and wherein the second optical add power is constant alongeach horizontal cross section in the second region; and a third regionhaving at least the first optical power and a plurality of third opticaladd powers comprising a progression of optical add powers increasingalong the vertical diameter from the first optical power to the secondoptical add power, wherein the third region comprises a central portionof said optic, wherein an uppermost boundary of the third region isabove a center of said optic and a lowermost boundary of the thirdregion is below the center of said optic, and wherein each of theplurality of third optical add powers is constant along a horizontalcross-section in the third region parallel to the horizontal diameter.2. The lens of claim 1, wherein the uppermost portion comprises at leastthe uppermost 25% along the vertical diameter of said optic.
 3. The lensof claim 1, wherein the uppermost portion comprises the uppermost 37.5%along the vertical diameter of said optic in the complete optic.
 4. Thelens of claim 1, wherein the second focus comprises a near vision focus.5. The lens of claim 1, wherein the lowermost portion comprises at leastthe lowermost 25% along the vertical diameter of said optic.
 6. The lensof claim 1, wherein the central portion comprises a centralmost of atleast 25% along the vertical diameter of said optic.
 7. The lens ofclaim 1, wherein the central portion comprises a centralmost of at least37.5% along the vertical diameter of said optic.
 8. The lens of claim 1,further comprising at least one haptic that at least partially supportssaid optic within a subject eye.
 9. The lens of claim 1, wherein theprogression of optical add powers in the third region is continuous. 10.The lens of claim 1, wherein the progression of optical add powers inthe third region is step-wise.
 11. The lens of claim 1, wherein theprogression of optical add powers in the third region is uniform. 12.The lens of claim 1, wherein the progression of optical add powers inthe third region is non-uniform.
 13. The lens of claim 1, wherein thethird region has a constant height measured along a vertical diameter ofthe optic.
 14. The lens of claim 1, wherein the third region isasymmetric with respect to the center of the optic.